In electrochemical grinding of this type, two distinct machining actions, in combination, are simultaneously carried out upon a workpiece: the mechanical abrading and scrubbing of the wheel surface against the workpiece and the electrolytic (anodic) dissolution of material from the workpiece by passage of a high-density electric current between the workpiece and the conductive or matrix portion of the wheel electrode across a gap produced by nonconductive abrasive protrusions on the conductive wheel matrix and supplied with a liquid electrolyte. As material removal proceeds in this manner, the wheel is advanced relatively to the workpiece and moved into the latter until a given depth is reached throughout the total machining region in the workpiece surface to produce a desired shape thereon.
Wheel electrodes, which should thus be satisfactory both in conductivity and mechanical properties, may be made by one of various techniques including: mixing abrasive particles with a conductive graphite or metallic powder and sintering the mixture into a coherent wheel body; mixing abrasive particles with powdery or flaky metal and bonding them together with the aid of a resinous binder; impregnating graphite, silver, copper or the like electrically conductive fine particles with a resinous binder into interstices of a porous abrasive body, e.g., vitrified or vitreous grinding wheel as prepared for mechanical grinding; and chemical plating of wall portions of interstices of such a porous abrasive body.
Heretofore, regardless of which one of these techniques is employed to prepare the wheel electrode or which type of wheel electrodes is to be utilized, efforts have been made to insure that the wheel has a uniform conductivity over the entire machining body or surface in order to afford an accurate shaping of the workpiece and better workpiece finish. In other words, it has been believed to be critical to insure that the abrasive protrusions projecting from the surface of the conductive wheel body be essentially of an equal thickness over the entire machining surface area of the wheel electrode independently of the nature and character of geometry of portions of the machining surface.
On the other hand, it has been recognized that in general, electromechanical grinding results are of a limited accuracy and much inferior to mechanical grinding in this respect. Thus, overcutting is a common occurrence in electrochemical grinding and could only be corrected by subsequent mechanical grinding with a separate grinding tool. Such overcutting typically occurs at corner, angular or edge portions of the machining surface and, even more significantly, at surface portions extending parallel to or essentially parallel to the feed direction of the wheel electrode relative to the workpiece or perpendicularly to the spindle carrying the rotating wheel electrode therearound.